US6634237B2 - Collection reservoir for use with flow meter control system - Google Patents

Abstract

A collection reservoir54includes a rigid-walled cassette adapted for connection to aspiration tubing50.The cassette also includes a pair of electrodes36positioned so that the electrodes are electrically connectable to a flow meter34.In operation, the electrodes are exposed to the fluid and tissue being aspirated from the surgical site so that the flow meter indicates a flow rate of the fluid and tissue from the surgical site.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to sensing an aspiration flow rate in a surgical pump system. More particularly, the present invention is directed towards a flow meter and control system for use with surgical pump systems.

2. Description of Related Art

The flow and flow rate of tissue and fluids through an aspiration tube is of interest during operations, including ophthalmic operations. However, direct measurement of the flow rate is typically impractical. Flow rates are generally inferred for positive displacement pumps, e.g., flow-based pumps that are based on pump rotation or other in-direct periodic measurements, these pumps are also commonly referred to as peristaltic pumps. Flow rates for venturi-based pumps have generally not been measured nor has an indirect measurement been used.

Measurement of the surgical aspiration flow rate may be valuable in that it can provide for safe control of the ophthalmic surgical equipment. In most positive displacement-based systems, flow has been known to be inferred from the cycle frequency, i.e., the rotation rate, of the aspiration pump. However, this inference may be invalid in situations where there are varying pressure differentials within the pump system. The pressure variations may occur as a result of changes in the irrigation-fluid bottle height, changes in the viscosity of the aspirant, and changing occlusion conditions at the distal end of the aspiration tube. For known venturi-based aspiration systems no flow measurement has previously been feasible, nor can flow be accurately inferred from the vacuum level. This is because the actual flow rate varies with the viscosity of the aspirant and the occlusion state of the aspiration tube.

In the prior art, it is possible to measure the flow rate in the aspiration tube with a positive displacement or venturi-based system or any other type of pump system using traditional flow sensors. These traditional flow sensors include paddle-wheel, hot-wire, or other devices which are deflected in the presence of fluid flow. However, these devices become contaminated or closed by the aspirant and cannot be reused on a different patient, thereby making the use of such sensors expensive.

Therefore, it would be desirable to have a low-cost flow sensor that could be inexpensively incorporated into a disposable or reusable system to directly measure flow rate. Such a flow measurement can enable new modes of operation, particularly for vacuum-based systems. One such application is the emulation of a flow-based pump by a vacuum-based pump using an additional control loop.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a prior art circuit diagram of a Hall-effect flow meter;

FIG. 2 is a partial cut-away view of a pump system in accordance with the present invention;

FIG. 3 is a front view of a surgical cassette inserted in a console in accordance with the present invention;

FIG.4. is a surgical cassette in accordance with one aspect of the present invention;

FIG. 5 is an illustration of an aspiration tube for connection to a surgical cassette in accordance with an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hall-effect flow meters for sensing the flow of conductive fluids are known. Such a prior art Hall-effect flow meter is shown in FIG.1. Theflow meter10 includes aconduit12 includingelectrodes14 that are in communication with the inner diameter ofconduit12 such that the electrodes are in contact withconductive fluids16 flowing throughconduit12. Amagnetic core18 is placed aroundconduit12 so as to induce an electromagnetic field perpendicular to a line-drawn throughelectrodes14. Transformer20 is connected todriver22 andoscillator24. Signals fromelectrodes14 are amplified byamplifier26, and the amplified signals are fed tosynchronous demodulator28. A signal representative of the flow rate of theconductive fluid16 is outputted tonode30.

Ophthalmic surgical systems can be broadly categorized as flow-based or vacuum-based. Flow-based pump systems attempt to maintain a constant or controlled rate of flow within specific vacuum ranges. A feedback or control loop may be used to ensure the constancy of the drive system under differing loads conditions. An additional feedback control loop may exist between a vacuum sensor in the aspiration line in the motor, to limit the amount of vacuum in the aspiration tube.

Vacuum-based systems also have feedback control loops, where the signal from a vacuum sensor in the aspiration path is compared to the pre-set desired vacuum level. Error signals are then sent to a vacuum generator, such as a proportional value and venturi chamber, to increase or decrease the vacuum level.

In certain situations, the emulation of a flow-based pump system by a vacuum-based pump system may be desirable. Such emulation has not been practical before the present invention, because there has been no practical means to measure flow rate in the vacuum-based system.

The present invention solution for ophthalmic aspiration flow rate measurement preferably utilizes an isolated Hall-effect electromagnetic flow meter, such as described above in FIG.1. The present invention, shown in FIG. 2, takes advantage of the fact that the saline solution commonly used in ophthalmic surgery is electrically conductive. Thus, a Hall-voltage can be induced across an aspiration tube if a magnetic field is applied. The flow meter34 (preferably similar to theflow meter10 of FIG. 1) in the ophthalmicsurgical pump system32 includes of a magnetic field source or electromagnetic magnet andmeter34 in use is connected to a disposable electrode assembly36 (as shown in FIGS.3-5).Control electronics assembly38, preferably responds to the output offlow meter34, to control a proportional value or venturi chamber (not shown) of aventuri pump56 to emulate a peristaltic pump by maintaining a constant flow rate of fluids and tissues through path ortube50. The preferred embodiment shows anaspiration tube50, but thetube50 could also be other pathways that allow fluids and tissues to be carried away from the surgical site.

FIG.2. further shows an irrigation-fluid bottle40 connected to anirrigation line42, witharrow44 showing the direction of travel of the saline fluid intohandpiece46.Surgical handpiece46 performs a surgical operation oneye48. Fluids frombottle40 and excised surgical tissue are aspirated fromeye48 through aspiration path50 (which is preferably standard surgical tubing) in the direction shown byarrow52. The aspirated fluid and tissue is received bycollection reservoir54 which is contained within pump56 (preferably a venturi pump though a peristaltic or other pump may be used as well). The venturi pump is preferably the same pump sold with Bausch & Lomb's Millennium® Ophthalmic Surgical System. Venturipump56 creates a vacuum level for aspirating fluid and tissue from the surgical site ateye48 to thecollection reservoir54. Theflow meter34 is electrically connected (connection shown at58) to controlcircuitry38, as well as being electrically connected to one of theaspiration tubing50 or thecollection reservoir54 as further described below.Control circuitry38 is connected to theflow meter34 and toventuri pump56 for varying the vacuum level of thepump56 and thereby maintaining a desired flow rate of the fluid and tissue being aspirated from the surgical site.

Preferably,collection reservoir54 is a rigid-walled cassette so that the cassette will be operable and not collapse during operation when a vacuum level is applied by theventuri pump56.Further collection reservoir54 is similar to cassettes currently sold by Bausch & Lomb except as modified and described in this invention.Electrodes36 are not visible in the view of FIG. 2 though may be seen in alternative embodiments in FIGS. 3-5.

FIG. 3 shows a partial front view of aventuri pump56 including acollection reservoir54 for use insurgical pump system32.Collection reservoir54 is preferably a rigid-walled cassette adapted for connection to theaspiration tubing50 and receives fluid and tissue aspirated from a surgical site.Collection reservoir54 also includes a pair ofelectrodes36 positioned so that the electrodes are electrically connectable to flowmeter34. During operation, theelectrodes36 are exposed to the fluid and tissue such that theflow meter34 shall indicate a flow rate of the fluid and tissue from the surgical site. Preferably,electrodes36 are positioned so that, in operation,electrodes36 align perpendicular to anelectromagnet60 thereby forming a Hall-effect flow meter. FIG. 4 shows a side elevation view of acollection reservoir54 as described above.Electrodes36 may be molded into thereservoir54 or inserted by any other known method, but in any case, the electrodes should form a sufficient seal withreservoir54 to prevent fluids from leaking.

FIG. 5 is an alternate embodiment of the present invention, whereinsurgical tubing62 is essentially the same astube50 except thattube62 includes a pair ofelectrodes64 for cooperation withelectromagnet60 andflow meter circuitry34 and is shown to be connectable with acollection reservoir66.Surgical tubing62 carries fluid to or from a surgical site and includes a pair of electrodes positioned within the tubing such that the electrodes, in operation, are exposed to the fluids and wherein the electrodes are electrically connectable to a flow meter for indicating a flow rate of the fluids through the tubing. Preferably, theelectrodes64 are positioned so that, in operation the electrodes are perpendicular to an electromagnet, such as that shown in FIG. 3, to form a Hall-effect flow meter.Electrodes64 may be molded intotubing62 or may be press fit and should form a liquid tight seal withtubing62.

Theflow meter34 provides a magnetic field required to produce the Hall-effect voltage. The magnetic driver can be constructed of a permanent or preferably an electromagnet. An electromagnet is preferred so that the magnetic field may be oscillated. Alternatively, the field may be oscillated by rotation of a fixed cylindrical magnet (not shown). In either configuration, an air gap is required so that the aspiration tube may be inserted within the magnetic field. Thedisposable electrodes64 or36 must be in contact with the aspirant. These electrodes may be molded into anaspiration tube60 as shown in FIG. 5, into acassette54 as shown in3 and4, or into areflux bulb68 at low cost. It is also noted that a Hall-effect flow meter as described, can be connected toirrigation tubing42 to provide an accurate flow rate of the saline solution into the eye.

Themetal electrodes36 or60 are in contact with the aspirated saline solution resulting in an electrochemical reaction, such as corrosion, which, in turn, produces electrical signals. The use of an alternating magnetic field from the Hall-effect flow meter induces alternating voltages. The amplitude of this alternating field is then correlated to a flow rate. Electrochemical voltages not associated with the flow rate are filtered and eliminated easily because they are steady currents.

Thus, there has been shown an inventive flow meter for an ophthalmic surgical pump system. This flow meter could be used with flow-based pumps or vacuum-based pumps as described above.

Important application using theflow meter34 in connection with the venturi-based pump system is the emulation of a positive displacement pump. The flow rate output ofmeter34 can be used in a feedback control loop to adjust the vacuum level. This feedback control loop is preferably part ofcontrol circuitry38. This control loop consists of measuring the flow rate withmeter34 and comparing that rate to the commanded flow rate. If the sense flow rate is lower than commanded, a vacuum generator level is increased to generate additional vacuum. This in turn increases the flow rate. Conversely, if the flow rate is too high, the vacuum generator level is decreased resulting in a decreased flow rate. In this way, using control system design the characteristics of a flow-based pump may be emulated usingventuri pump56. With or without a feedback control loop, it is preferred that the flow rate detected byflow meter34 be displayed (not shown) bypump system32.

An additional application offlow sensor34 is occlusion detection. Essentially, occlusion detection is simply another flow rate detection scheme where the flow rate detected approaches zero (0) when tissue blocks the tip of a surgical device or the aspiration tube. When the flow rate approaches zero (0) dangerous conditions result such as overheating of the surgical device or occlusion of the aspiration pathway and quick detection of such a condition is highly desirable. Therefore, detection of a flow rate approaching zero (0) could be used to warn the user (audibly or visually) that the system has an occlusion or upon detection the aspiration could be slowed or stopped. As those skilled in the art will appreciate, the detection and warning of a flow rate need not be at zero (0), but could occur at some flow rate above zero (0), but where overheating may still be of concern.

Thus, there has been shown an inventive ophthalmic surgical pump system providing a low-cost aspirant flow meter. In addition, such a system may be used in other surgical pump systems, such as endoscopic pumps.

Claims (2)

We claim:

1. A collection reservoir for use in a surgical pump system comprising:

a rigid-walled cassette adapted for connection to an aspiration tube and for receiving fluid and tissue aspirated from a surgical site; and

a pair of electrodes molded into the cassette and positioned so that the electrodes are electrically connectable to a flow meter wherein the electrodes, in operation, are exposed to the fluid and tissue such that the flow meter indicates a flow rate of the fluid and tissue from the surgical site without the electrodes interfering with the flow of fluid and tissue through the cassette.

2. The reservoir ofclaim 1 wherein the electrodes are positioned so that, in operation, the electrodes align with an electromagnet thereby forming a Hall-Effect flow meter.

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